Animation Problem: Baking an Action creates a bad scaling animation
You need to delete all the scale keyframes of the bone called DEF-spine.006.
Also, you've keyframed the scale of several bones that are its parents (neck bones called DEF-spine.005 and DEF-spine.004), so you either need to disable the DEF-spine.006 Inherit Scale option, or you need to delete the scale keyframes of these other bones.
Also, make sure they are all at a scale of 1 (AltS).